In carburetors of this type it is necessary to move the throttle means (throttle valve) and the starter means (choke valve) to a defined start position for cold starting of the engine. To this end, the prior art carburetors usually are provided with actuating members for the throttle and choke valves. In one type of such carburetors, the actuating member of the throttle valve has a detent member locking the throttle valve in its start position. Due to manufacturing tolerances of the force transmitting mechanism between the throttle valve and its actuating member, it is difficult, if not impossible, to obtain a precisely defined start position of the throttle valve; actually the start positions of the throttle valves of different carburetors vary within a relatively large range of manufacturing tolerances.
German patent application 27 06 389 discloses a carburetor wherein the throttle valve is held in its start position by a holding member. The holding member which comprises a lever cooperates with the throttle valve via detent means such that it displaces the throttle valve into its start position and holds it therein until the detent means is released due to displacement of the throttle valve. The holding member is returned to its rest position by a return spring. In this carburetor the holding member and the choke valve are interlinked so that the holding member is moved into its start position by the actuating member of the choke valve, and the holding member when being returned moves the choke valve into its rest position.
The holding member coupled to the choke valve and directly cooperating with the throttle valve provides for a precisely defined start position of the throttle valve. If, however, in this carburetor the throttle valve, for warm starting of the engine, is moved into its start position by the holding member, it is inevitable that also the choke valve is moved into its cold start position due to the coupling between the choke valve and the holding member; such movement of the choke valve to its cold start position is, of course, not desired for warm starting of the engine.
It is an object of the present invention to provide a carburetor for an internal combustion engine in particular of a chain saw or the like wherein the throttle means is adapted to be moved into a precisely defined start position while an undesired displacement of the starter means in case of warm starting the engine should be avoided.
To this end, a carburetor for an internal combustion engine, in particular of a chain saw, includes throttle means biased towards an idle position and adapted to be displaced by a first actuating member, and includes also starter means adapted to be displaced between start and rest positions by a second actuating member, and holding means which, when actuated, moves the throttle means to a start position and holds the throttle means in the start position via detent means. The detent means is released by the first actuating member when the throttle means continues to be displaced such that the holding means returns into its rest position under the action of return spring means. The above concept is characterized in that the holding means is operatively separate from the starter means and arranged to be actuated by a third actuating member.
Due to the holding means being operatively separate from the starter means, the throttle valve, for warm starting the engine, may be moved into its start position via the actuating member of the holding means without the necessity of displacing the starter means. Nevertheless, the start position of the throttle means is precisely defined by the holding means.